Matt Pharr

Bio: Matt Pharr is an academic researcher from Texas A&M University. The author has contributed to research in topics: Lithium & Medicine. The author has an hindex of 25, co-authored 58 publications receiving 3929 citations. Previous affiliations of Matt Pharr include University of Illinois at Urbana–Champaign & Harvard University.

Lab-on-Skin: A Review of Flexible and Stretchable Electronics for Wearable Health Monitoring

Abstract: Skin is the largest organ of the human body, and it offers a diagnostic interface rich with vital biological signals from the inner organs, blood vessels, muscles, and dermis/epidermis. Soft, flexible, and stretchable electronic devices provide a novel platform to interface with soft tissues for robotic feedback and control, regenerative medicine, and continuous health monitoring. Here, we introduce the term “lab-on-skin” to describe a set of electronic devices that have physical properties, such as thickness, thermal mass, elastic modulus, and water-vapor permeability, which resemble those of the skin. These devices can conformally laminate on the epidermis to mitigate motion artifacts and mismatches in mechanical properties created by conventional, rigid electronics while simultaneously providing accurate, non-invasive, long-term, and continuous health monitoring. Recent progress in the design and fabrication of soft sensors with more advanced capabilities and enhanced reliability suggest an impending t...

Fracture of electrodes in lithium-ion batteries caused by fast charging

Abstract: During charging or discharging of a lithium-ion battery, lithium is extracted from one electrode and inserted into the other. This extraction-insertion reaction causes the electrodes to deform. An electrode is often composed of small active particles in a matrix. If the battery is charged at a rate faster than lithium can homogenize in an active particle by diffusion, the inhomogeneous distribution of lithium results in stresses that may cause the particle to fracture. The distributions of lithium and stress in a LiCoO2 particle are calculated. The energy release rates are then calculated for the particle containing preexisting cracks. These calculations predict the critical rate of charging and size of the particle, below which fracture is averted.

Lithium-Assisted Plastic Deformation of Silicon Electrodes in Lithium-Ion Batteries: A First-Principles Theoretical Study

Abstract: Silicon can host a large amount of lithium, making it a promising electrode for high-capacity lithium-ion batteries. Recent experiments indicate that silicon experiences large plastic deformation upon Li absorption, which can significantly decrease the stresses induced by lithiation and thus mitigate fracture failure of electrodes. These issues become especially relevant in nanostructured electrodes with confined geometries. On the basis of first-principles calculations, we present a study of the microscopic deformation mechanism of lithiated silicon at relatively low Li concentration, which captures the onset of plasticity induced by lithiation. We find that lithium insertion leads to breaking of SiSi bonds and formation of weaker bonds between neighboring Si and Li atoms, which results in a decrease in Young's modulus, a reduction in strength, and a brittle-to-ductile transition with increasing Li concentration. The microscopic mechanism of large plastic deformation is attributed to continuous lithium-assisted breaking and re-forming of SiSi bonds and the creation of nanopores.

Large Plastic Deformation in High-Capacity Lithium-Ion Batteries Caused by Charge and Discharge

Abstract: Evidence has accumulated recently that a high-capacity electrode of a lithium-ion battery may not recover its initial shape after a cycle of charge and discharge. Such a plastic behavior is studied here by formulating a theory that couples large amounts of lithiation and deformation. The homogeneous lithiation and deformation in a small element of an electrode under stresses is analyzed within nonequilibrium thermodynamics, permitting a discussion of equilibrium with respect to some processes, but not others. The element is assumed to undergo plastic deformation when the stresses reach a yield condition. The theory is combined with a diffusion equation to analyze a spherical particle of an electrode being charged and discharged at a constant rate. When the charging rate is low, the distribution of lithium in the particle is nearly homogeneous, the stress in the particle is low, and no plastic deformation occurs. When the charging rate is high, the distribution of lithium in the particle is inhomogeneous, and the stress in the particle is high, possibly leading to fracture and cavitation.

Concurrent Reaction and Plasticity during Initial Lithiation of Crystalline Silicon in Lithium-Ion Batteries

Abstract: In an electrochemical cell, crystalline silicon and lithium react at room temperature, forming an amorphous phase of lithiated silicon. The reaction front—the phase boundary between the crystalline silicon and the lithiated silicon—is atomically sharp. Evidence has accumulated recently that the velocity of the reaction front is limited by the rate of the reaction at the front, rather than by the diffusion of lithium through the amorphous phase. This paper presents a model of concurrent reaction and plasticity. We identify the driving force for the movement of the reaction front, and accommodate the reaction-induced volumetric expansion by plastic deformation of the lithiated silicon. The model is illustrated by an analytical solution of the co-evolving reaction and plasticity in a spherical particle. We derive the conditions under which the lithiation-induced stress stalls the reaction. We show that fracture is averted if the particle is small and the yield strength of lithiated silicon is low. Furthermore, we show that the model accounts for recently observed lithiated silicon of anisotropic morphologies.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Table Of Integrals Series And Products

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